Anamorphic optical systems provide different magnifications in mutually perpendicular planes containing the optical axis. They can be utilized for special purposes to impart a deliberate and controlled degree of distortion in optical images. Anamorphic systems are not new, in fact the Patent literature goes back at least as far as 1898 when British Pat. No. 8512 disclosed achromatization of prism type anamorphs. In 1929 the French Scientist Henri Chretien demonstrated a system for motion pictures in which a very wide picture was compressed laterally in the camera by means of a cylindrical lens arrangement. On subsequent projection the image was expanded laterally by means of a similar type lens. In this case an object with an aspect ratio of 2.6:1 could be recorded in a normal motion picture camera equipped with an imaging system capable of handling a 2:1 aspect ratio. The system was first used commercially by Twentieth-Century Fox in 1952 and is generally known as the "Cinemascope" system.
There are two main types of anamorphic systems, the prismatic and the cylindrical forms. The prismatic type of anamorph depends for its action upon the compression of a beam of light as it passes through a prism. If the width of the entering beam is D and that of the emergent beam is D.sub.1, then the magnification ratio M is equal to D.sub.1 /D. This is also equal to the magnification ratio of the prism. If the angle between the two beams when they enter the prism is A then the angle between the emergent beams is M times A. If a prism is used in a position decidedly away from the minimum deviation condition, the emergent beam will be either broader or narrower than the entering beam. If two prisms are utilized the deviation of light by one prism is rectified by the other, but each prism contributes its share to the anamorphic compression. Axial rays emerge from the system parallel to their direction of incidence.
In an actual system where spherical lenses are incorporated it is necessary to compensate for optical aberrations. Each prism set is thus achromatized by using two or more elements of different materials. Prism anamorphs are free from axial astigmatism, but only when used in parallel light.
The cylindrical type of anamorphic attachment assumes, in its simplest form, two cylindrical lenses. In practice it is necessary to achromatize the positive and negative cylindrical lenses. This is effected by combining different types of glass in each component in the same way that lenses with spherical surfaces are achromatized by using crown and flint glass. The axes of the various cylindrical surfaces must be precisely aligned to prevent astigmatism so that a sharp focus can be obtained.
Anamorphic optical systems in which the magnifications in mutually perpendicular planes containing the optical axis are different are thus not new. Their application has however been severely limited by the difficulties in applying routine lens design procedures to the unusual and asymmetric conditions which they must assume. In addition, the problems of manufacturing these lenses, which contain either prisms or cylinders are considerable.
In the printing industry it is desirable to reduce the size of an object in one direction while maintaining the same size in a mutually orthogonal direction. This change in the proportions of the image can be used to fit varying originals into a common printing format or to reduce paper consumption. In doing this no appreciable loss of image quality can be tolerated particularly with respect to imaging points, such as half tone dots. Systems have been proposed and are indeed being used at the present time. However, these systems usually take the form of attachments to conventional lenses. Such attachments substantially degrade image quality and are not normally capable of operation at more than one anamorphic magnification and even under these conditions refocusing is required.